Australia's general election is "too close to call" and the final result may not be known for days as counting continues for tightly contested seats, Labor Party leader Bill Shorten has said.

With 75.2 percent of the votes counted, the Liberal-National coalition is leading with 72 seats and the Labor Party is close behind with 66, the Australian Broadcasting Corporation has reported.

Seven seats are not decided and other parties, including independents hold five.

Australians to vote in tight election race

For a majority win, 76 seats are needed but if neither party receives enough votes, support will be needed from other parties or independents.

Opinion polls have suggested that public frustration with the coalition and Labor may prompt an unusually high number of votes for minor parties, such as the Greens.

That raises the prospect that neither the coalition, nor Labor, will have enough seats to win an outright majority, resulting in a hung parliament.

Prime Minister Malcolm Turnbull, however has said that he is confident his Liberal/National coalition can form a majority, but opposition challenger Shorten has criticised the incumbent, saying he has lost the people's mandate for his agenda.

"It's a very, very close count," Turnball told his supporters in Sydney on Saturday. "I can report that based on the advice I have from the party officials, we can have every confidence that we will form a coalition majority government in the next parliament."

Still, there were rumblings about Turnbull's future given the closeness of the vote.

Peter Hartcher, a political editor at theSydney Herald, told Al Jazeera: "It's more likely that Turnball will hang on to power with a much reduced majority.

"The country is having a great deal of trouble putting its trust in either of the parties. The incumbent government is portraying it as a question of, almost entirely, economics."

Al Jazeera's Andrew Thomas, reporting from a polling station in Sydney, said: "It seemed that Turnball had a pretty healthy lead going into the campaign." Since then, however, polls have tightened, Thomas added.

Analysts say it is highly unlikely that Labor will gain the 21 seats it needs to form a majority government in the 150-seat House of Representatives - Labor currently holds 55 seats, but polls say the race will be tight.

"There is one thing for sure - the Labor party is back," Shorten, who has campaigned hard on health and education, told his supporters in Melbourne

"Three years after the Liberals came to power in a landslide, they have lost their mandate," he added, pointing to Tuesday as the likely day when a final outcome is known.

Turnball's government has focused much of its campaign on a promise to generate jobs and economic growth through tax cuts to big businesses.

Australia economy sees signs of tougher times

Economic growth is a key issue for many Australians, who have seen thousands of jobs vanish from the country's once-booming resources sector amid China's industrial slowdown.

Labor has that said it will keep the higher tax rates and use the revenue to better fund schools and hospitals.

Same-sex marriage has also emerged as a campaign issue.

Turnbull, who personally supports gay marriage despite his party's opposition to it, has promised to hold a national poll known as a plebiscite this year that will ask voters whether the nation should allow same-sex marriage.

But governments are not bound by the results of plebiscites, and some conservative politicians have said they will vote down a gay marriage bill - even if most Australians supported marriage equality.

Labor, which dubbed the plebiscite a waste of taxpayers' money, promises that the first legislation the party will introduce to parliament will be a bill legalising same-sex marriage.

Shorten, pictured, played a key role in ousting two of the Labor Party's own prime ministers in the space of three years [EPA]